1. Field of the Invention
This invention relates to improvements in a cutting and processing method that uses a wire saw for cutting such hard and brittle materials as ceramics and silicon used in the manufacture of semiconductor devices. The present invention further relates to a semiconductor material cutting and processing method wherewith, by performing the cutting using wire in which abrasive particles are made to adhere to the outer circumference of a core wire, and using either a slurry that is a mixture of free abrasive particles and an oil base or aqueous solution base, or an alkaline solution, the total thickness variation (TTV) in the wafers obtained can be diminished, the residual processing distortion reduced, the process stress suppressed, and the cutting heat suppressed.
2. Description of the Prior Art
In manufacturing wafers that are semiconductor substrate materials, wire saw cutting apparatuses that cut the wafers with traveling wires from a cylindrical silicon monocrystal ingot are widely used.
To describe an example configuration of a wire saw cutting apparatus used for cutting silicon monocrystal ingots, as diagrammed in FIG. 1, for example, a wire is deployed so that it is wound parallel, at a constant interval, about the outer circumferences of three horizontally placed long rollers, and wire fed from one wire bobbin is taken up on another wire bobbin after it has traveled around the outer circumferences of the rollers.
With the wire segments arrayed in the axial direction between the two upper rollers at a constant interval and traveling in the same direction, the silicon monocrystal ingot is secured in a jig, and the jig, in a condition wherein it is mechanically held by a separate holding mechanism, is lowered so that the monocrystal ingot is pressed against the wire segments, and cut. In addition to those which lower the monocrystal ingot, there are also configurations which cut the ingot by pressing it against the wire segments while raising it.
One of the methods of using a wire saw cutting apparatus having the structure described above is a method that employs free abrasive particles, performing the cutting while supplying to both ends of the cut surfaces on a slurry wherein a certain quantity of polishing powder is mixed into an oil or aqueous base (Japanese Utility Model Application Laid-Open No. S57-193349/1982). There is also a method that employs adhering abrasive particles, wherewith the ingot is directly cut using a wire wherein abrasive particles are secured by a bonding agent to a wire filament or metal-deposited thereto (Japanese Patent Application Laid-Open No. H11-42548/1999).
Also proposed, with the object of reducing post-cutting residual distortion, is a method of cutting that uses a nylon, polyester, or other resin filament instead of the metal wire noted above, or such a resin filament which has been reinforced with carbon or glass fiber, using simple water as the coolant fluid (Japanese Patent Application Laid-Open No. H8-126953/1996).
Because work consisting of brittle material is cut with wire consisting of piano wire of high tensile strength and hardness, when the cutting is done using adhering abrasive particles, the process stress generated is great, wherefore there is a problem in that residual process distortion becomes great.
In the case of cutting using free abrasive particles, there are a number of problems, such as that the work environment is made poor by the slurry used splashing about, as that the roughness of cut surfaces is poor because cutting is done while carrying the slurry on the wire, and as that variation in wafer thickness occurs depending on the amount of slurry carried in.
The methods that use a resin filament are not necessarily methods that are outstanding in industrial production applications in terms of cutting process efficiency.
An object of the present invention is to provide a cutting and processing method for semiconductor materials that either cuts semiconductor materials such as silicon ingots, or makes grooves therein, using a wire saw, wherewith there is little residual process distortion after cutting, and wherewith high-quality, high-precision processed products exhibiting outstanding thickness precision can be stably obtained.
The inventor conducted various investigations with the object of devising a cutting method capable of suppressing the occurrence of residual process distortion in order to resolve the problem of the unavoidable occurrence of residual process distortion in processed products after cutting with conventional wire saws that use wires to which abrasive particles adhere to the outer circumference of a core wire, as described in the foregoing. As a result, the inventor discovered that by cutting with a wire to which fixed abrasive particles adhere while concurrently using a specific slurry, the process stress occurring at the time of fixed abrasive particle cutting is cancelled out by the wrapping effect produced by the slurry, making low-distortion process cutting possible.
The inventor also discovered that by performing cutting processing using a mixture of free abrasive particles and an oil base such as mineral oil in the slurry, the effects of enhancing cuttability, reducing residual process distortion, and suppressing process stress are high, and that by performing cutting processing using a mixture of free abrasive particles and an aqueous solution base such as PEG (polyethylene glycol material) therein, the effects of enhancing cuttability, reducing residual process distortion, suppressing process stress, and suppressing cutting heat are high.
The inventor further discovered that wafers exhibiting low distortion can be obtained by performing cutting while eliminating the process stress generated during cutting (residual distortion), by cutting an ingot while applying thereto an alkaline solution of KOH or NaOH generating 2% or lower process stress during cutting, and thus the present invention was perfected.
As based on the present invention, in a cutting and processing method based on a wire saw wherein abrasive particle treated wire wherein abrasive particles have been made to adhere to a core wire is used, it becomes possible to conduct low-distortion cutting and processing using the wrapping effect realized by cutting and processing using a slurry containing free abrasive particles, to counteract the process stress (residual distortion) generated in the cutting and processing, and low-distortion process cutting like that described above becomes possible by applying an alkaline solution, whereupon the process cost (process volume) in subsequent processing can be reduced.
In a cutting and processing method based on a wire saw using conventional abrasive particle treated wire, there are only the fixed abrasive particles, wherefore cutting tends to be done while having a damage layer below the wafer surface, and the process volume tends to become great in subsequent processes such as wrapping.
With the method of the present invention, however, as to the damage that occurs with cutting, the residual distortion becomes very slight, due to the fact that a wrapping effect is employed or selective etching is performed, and it becomes possible to sharply reduce process costs in subsequent processing. Another advantage realized is that TTV at the cut surfaces becomes small.